Isolated peripheral blood human granulocyte chromatin was used to elicit antisera specific for human neutrophilic granulocyte nuclear antigens. The following areas will be investigated: (1) Antigens will be isolated, characterized and their localization within the chromatin structure will be determined. (2) Immunocytochemical methods revealed that all late stage myeloid cell nuclei contained antigens. To further elucidate a possible role in cellular differentiation, the antigens will be studied in cultures of myeloid leukemic cells, both induced and non-induced to differentiate. Antigens will be studied in cultured cells as well as specimens of myeloid leukemia separated into early and late stage cells by density gradient centrifugation. (3) The normal myeloid chromatin antigens were found in chromatin from specimens of CML and AML. Chromatin isolated from a cell culture of acute promyelocytic leukemia contained only one of the three normal myeloid antigens. No cross-reacting antigens have been found in any other leukemias. The usefulness of the antisera in differentiating types of leukemias or in monitoring therapy will be determined by comparing the immunocytochemical reaction with the results of currently used diagnostic methods. (4) New antisera will be developed to chromatin antigens of other hematopoietic cells, both normal and transformed.